Study On The Rheological Properties Of Epoxy Resin Matrix Composites And Underfill Technology

The underfill process can reduce the deformation caused by the mismatch of the thermal expansion coefficient between the chip and the substrate,so that it is a key process to improve the stability of the packaging technology.The rheological properties of the underfill material are important factors for the filling process.Therefore,this paper is aim to study the rheological properties of the epoxy resin composite materials and the underfill process,and following work was mainly carried out:(1)The viscosities of epoxy resin and its composites were measured,and the constitutive model of the relationship between the content of additives and the viscosity of the composites was established.Through analyzing their rheological properties,epoxy resin and alumina/epoxy resin composites were Newtonian fluids.Carbon nanotubes/epoxy composites and two-phase filled composites were Pseudoplastic fluids.The addition of alumina and carbon nanotubes increases the viscosity of the matrix material.(2)Based on the Washburn model,we established an analytical model to predict the capillary-driven underfill process.This model is more reasonable to consider the impact of the solder ball on the flow,and the different contact angle of the fillers on the solder ball surface,chip and substrate surface.(3)Based on the analytical model,the influence of filling parameters and process parameters on the flow rate was analyzed.The higher the viscosity of filling material is,the faster the filling flows.When the viscosity is less than 20 Pa.s,the reduce of the flow rate is more obvious.Considering the rheological properties of the composites,we find that the higher the content of the additive,the slower the filling rate,so that the flow rate can be increased by reducing the amount of the additive.The greater the surface tension and the smaller the contact angle of filling material,the faster the filling speed.In addition,controlling the gap height between the chip and substrate near the turning point,reducing the ball size or increasing the bitch can also improve the flow rate effectively.(4)Based on the Fluent software,a three-dimensional numerical model of the underfilling flow is established.The influence of "boundary effect" on the flow front is studied by using this model.It is found that the flow on the sides is faster than the middle part.But the "border effect" is not easy to lead to the formation of fusion pattern and other defects.Therefore,there is no need to pay too much attention to the "border effect" when designing the chip.(5)We used the numerical model to simulate the underfilling flow of different dispensing.It is found that the potential defects of products under type I-type and L-type dispensing are small,while it is larger under U-type dispensing.